The
Delphi Method

The Delphi Method is a method of gaining consensus within a group,
which may be used to agree on task duration estimates. This is performed
by first asking for task estimates, then sending a summary of responses
back out to the team members, inviting them to modify their views in light
of this feedback. This is repeated until sufficient consensus is reached.

A simple method of finding a 'middle point' from the
final set of estimates is to use the following formula: